Effects of sessile whitefly nymphs (Homoptera: Aleyrodidae) on leaf-chewing larvae (Lepidoptera: Noctuidae)

The wide distribution, polyphagy, and the often severe effects of whiteflies, Bemisia spp., on their host plants cause a great potential for interspecific interactions between whiteflies and other insect herbivores. Feeding of the silverleaf whitefly, B. argentifolii Bellows & Perring, on collards, Brassica sp., induced high levels of pathogenesis-related proteins (e.g., chitinase, beta-1,3-glucanase, peroxidase, and lysozyme) that are considered to play defensive roles against phytopathogens and insect pests. Total protein contents, however, were comparable with those of control plants. Development of cabbage looper larvae, Trichoplusia ni (Hubner), was 20.8% slower on whitefly-infested leaves than on control leaves; relative growth rate was reduced by 18% (P much less than 0.01). Final larval weight and survival were not affected by whiteflies. When feeding on whitefly-infested leaves, larvae were found more frequently on the adaxial side of the leaf, which is whitefly-free. The data suggest that early-instar cabbage looper larvae are negatively affected by whitefly infestations, but older instars become omnivores, consuming plant material as well as immature whiteflies. In the field, only 4% of the loopers survived to pupation on whitefly-infested plants, but 18% survived on the whitefly-free plants. The data emphasized the importance of the looper's larval stage in inter-specific interaction and stressed the potentially significant effect of whiteflies on other herbivores in agroecosystems.